Crosslinkable rubber composition

ABSTRACT

It is sometimes desirable to cure rubber compositions utilizing non-sulfur curing agents. The subject invention reveals rubber compositions which can be cured without utilizing sulfur or sulfur containing compounds. The subject invention more specifically disclosed a rubber composition which can be crosslinked by heating which is comprised of (1) at least one rubber having pendant blocked isocyanate groups bound thereto; and (2) at least one compound which contains at least 2 Zerewitinoff active hydrogens. 
     This invention also discloses crosslinking of elastomer compounds containing (1) at least one rubber having functionalized groups containing at least one Zerewitinoff active hydrogen and (2) at least one compound which contains at least two blocked isocyanate groups. This invention also discloses self-curing elastomers containing both blocked isocyanate groups and groups containing at least one active Zerewitinoff hydrogen.

BACKGROUND OF THE INVENTION

Elastomers can be crosslinked by a number of techniques as described byA. Coran in "Science and Technology of Rubber" Chapter 7. Mostelastomers are cured using sulfur or peroxide vulcanization althoughcuratives such as phenolic resins, quinone derivatives, maleimidederivatives and metal oxides can also be employed in the crosslinkingreaction.

A novel crosslinking reaction was reported in Kautschuk GummiKunststoffe 8/83 which discloses a cure system consisting of the adductof a diisocyanate with nitrosophenol. In this cure system, thenitrosophenol is released at cure temperature and reacts with theelastomer. Crosslinking occurs when the diisocyanate reacts withfunctionality on the polymer bound nitrosophenol. This blockedisocyanate curative is incorporated in a step separate from thepolymerization.

Polymer bound isocyanates have been used as part of a curing package ofacrylate polymers. European Patent Application Publication No. 130,322discloses that acrylate polymers containing m-isopropenyl α,α-dimethylbenzylisocyanate (TMI) can be cured and that the polymers can be used incoating applications. U.S. Pat. No. 4,694,057 discloses that elastomerscontaining small amounts of1-(1-isocyanato-1-methylethyl)-3-(1-methylethenyl)- benzene (TMI) can becrosslinked by utilizing difunctional or polyfunctional active hydrogencompounds. For instance, U.S. Pat. No. 4,694,057 discloses thatelastomers which are difficult to cure with sulfur or sulfur containingcompounds, such as polychloroprene, can be cured utilizing such atechnique. However, neither the teachings of European Patent PublicationNo. 130,322 or U.S. Pat. No. 4,694,057 suggest any advantage that can berealized by blocking the isocyanate groups in the elastomer. In fact,neither of the subject references disclose the possibility of curingsuch compounds which contain blocked isocyanate groups. Problemsassociated with premature crosslinking have hindered the commercialdevelopment of cure systems which rely on crosslinking through unblockedisocyanate groups in elastomers.

SUMMARY OF THE INVENTION

This invention discloses a technique for curing rubber compositionswhich does not rely upon sulfur or sulfur containing compounds. The curesystems of the subject invention rely upon the reaction between ablocked isocyanate group and an active Zerewitinoff hydrogen atom. Theutilization of the process of this invention accordingly results in aurethane or urea type cure. One benefit realized by utilizing theprocess of this invention is that premature crosslinking of theelastomer is generally not a significant problem if the appropriateblocking group is used.

The subject invention more specifically discloses a rubber compositionwhich can be crosslinked by heating which is comprised of (1) at leastone rubber having pendant blocked isocyanate groups bound thereto; and(2) at least one compound which contains at least 2 Zerewitinoff activehydrogens.

The subject invention also reveals a rubber composition which can becrosslinked by heating which is comprised of (1) at least one rubberhaving Zerewitinoff active hydrogens bound thereto: and (2) at least onecompound having at least 2 blocked isocyanate groups bound thereto.

The subject further discloses a rubber composition which can becrosslinked by heating which is comprised of polymer chains having (1)pendant blocked isocyanate groups bound thereto; and (2) Zerewitinoffactive hydrogens bound thereto.

There are different requirements for each of the previous approaches. Inall cases the polymer must not undergo premature crosslinking during thepolymer drying step or when the polymer is mixed with other ingredientsnecessary for good elastomeric compounds. These polymers are generallyprepared by an emulsion process and must be coagulated and dried. Incommercial operations, emulsion polymers are dried at 200-230° F. forapproximately 45 minutes. This polymer is then mixed with carbon blackin a non-productive mix at 300-330° F. for 1-3 minutes. The curative isadded to the rubber from the non-productive mix in a productive mix at220° F. Thus, polymers containing the blocked isocyanate functionalitycannot undergo extensive deblocking at drying conditions or during thenon-productive mix or the material will become unworkable. In the casewhere the polymer contains the Zerewitinoff active hydrogen, prematurevulcanization is not a problem. The blocked isocyanate compound curativemust only be stable to the productive mix which takes place at 220° Ffor 1-2 minutes.

The following reaction depicts the curing of a rubber having pundantblocked isocyanate groups bound thereto with a purative which containstwo Zerewitinoff active hydrogent. In the first step of the reaction,the blocking agent represented as X is removed from the isocyanate groupby the action of heat as follows: ##STR1## wherein P represents polymerchains of the rubber. In the second sage of the curing reaction, thecurative containing two active Zerewitinoff hydrogens reacts with thefree isocyanate groups on two different polymer chains of the rubberbeing cured. This reaction is depicted as follows: ##STR2## wherein Arepresents an alkylene group or an arylene group. The same basicreactions are utilized in curing rubbers having active Zerewitinoffhydrogens bound thereto with curatives containing at least two blockedisocyanate groups. In such reactions, the heat utilized to cure therubber causes the blocking group to be removed thereby creating a freeisocyanate group which is then available to react with activeZerewitinoff hydrogens on the rubber. Similarly, identical reactionstake place wherein the rubber being cured contains both pendant blockedisocyanate groups and active Zerewitinoff hydrogen atoms. In such cases,it is, of course, not necessary to utilize a separate curative. In otherwords, rubbers which contain both pendant blocked isocyanate groups andZerewitinoff active hydrogen atoms have a built in cure package.

Rubbers having pendant blocked isocyanate groups bound thereto can beprepared utilizing a wide variety of techniques. For instance, U.S. Pat.No. 4,429,096 discloses a process wherein the isocyanate group onmeta-TMI is blocked with a cationic carbamic structure and thenpolymerized into a polymer. The technique disclosed in U.S. Pat. No.4,429,096 is highly suitable for preparing rubbers having pendantblocked isocyanate groups which can be utilized in accordance with theprocess of this invention. U.S. Pat. No. 4,604,439 also discloses atechnique for incorporating blocked TMI into polymers utilizing emulsionpolymerization. The teachings of U.S. Pat. No. 4,429,096 and U.S. Pat.No. 4,604,439 are incorporated herein by reference in their entirety.U.S. Pat. No. 4,694,057 discloses a technique for polymerizing unblockedTMI into rubbers utilizing an emulsion polymerization technique. Suchrubbers containing unblocked TMI can be blocked by reacting the rubbercontaining unblocked TMI with an appropriate blocking agent. In fact,any rubber containing pendant unblocked isocyanate groups can be blockedby reacting the unblocked isocyanate groups thereon with an appropriateblocking agent.

A wide variety of compounds can be utilized to block isocyanate groupsin accordance with the process of this invention. Some representativeexamples of suitable compounds for utilization as blocking agentsinclude phenols, oximes, caprolactam, pyrrolidone, mercaptans and β-ketoesters. Blocking agents which can be utilized are discussed in greaterdetail in Z. Wicks, Journal of Coatings Technology, "Progress in OrganicCoatings", Vol. 5, page 73 (1975) and Z. Wicks, Journal of CoatingsTechnology, "Progress in Organic Coatings", Vol. 9, page 3 (1981), whichare incorporated herein by reference in their entirety.

The blocking agents which are preferred for utilization in the processof this invention include alcohols, cyclic amides, ketoximes, phenols,and secondary amines. The cyclic amides which can be utilized typicallyhave the structural formula: ##STR3## wherein n is an integer from 2 toabout 10. It is normally preferred for n to be an integer from 3 to 5.Caprolactam which has the structural formula: ##STR4## and a deblockingtemperature which is within the range of about 110° C. to about 140° C.and 2-pyrrolidone which has the structural formula: ##STR5## and adeblocking temperature which is within the range of about 160° C. toabout 190° C. are highly preferred blocking agents.

The ketoximes which can be utilized as blocking agents typically havethe structural formula: ##STR6## wherein R represents an alkyl groupcontaining from 1 to 10 carbon atoms and wherein R' represents ahydrogen atom or an alkyl group containing from 1 to 10 carbon atoms.Phenol and substituted phenols can also be utilized as the blockingagent. The secondary amines which can be utilized as blocking agentstypically have the structural formula:

    R--NH--R∝

wherein R represents an aryl group and wherein R∝ represents an aryl oran alkyl group.

A rubber having pendant blocked isocyanate groups bound thereto wherein2-pyrrolidone is utilized as the blocking agent is depicted as follows:##STR7## wherein P represents polymer chains of the rubber.2-pyrrolidone is a particularly valuable blocking agent because it has adeblocking temperature which is within the range of about 160° C. toabout 190° C. When the blocked isocyanate is heated to the deblockingtemperature, the blocking group is released exposing the freeisocyanate. The free isocyanate then undergoes the curing reaction. Incases where the isocyanate is not blocked, premature crosslinkingreactions occur making processing of the elastomer difficult if notimpossible. Different blocking groups can be employed depending on whatprocessing and curing temperatures are desired. If the rubber isprocessed at temperatures higher than the deblocking temperature,premature crosslinking or scorch of the rubber will occur. The higherthe deblocking temperature is, the more latitude there is in processingof the rubber but cure temperatures must, of course, be higher in orderfor deblocking and subsequent crosslinking to occur. As the deblockingtemperature is lowered, the rubber must be processed more gently but canbe effectively cured at a lower temperature. Thus, the deblocking groupcan be chosen to give the optimal mix of scorch safety and curetemperature. The deblocking temperature of 2-pyrrolidone has been foundto be very good in some applications. The deblocking temperature ofcaprolactam is somewhat lower but can also be used effectively as ablocking agent in curing some rubber compounds.

Zerewitinoff active hydrogen is reactive as determined by theZerewitinoff method as described in the Journal of the American ChemicalSociety, Vol. 49, page 3181 (1927). The Zerewitinoff active hydrogenwill typically be present in a hydroxyl group, amine group, carboxylgroup or thiol group. Zerewitinoff hydrogens which are present inhydroxyl groups are the most highly preferred. Zerewitinoff hydrogenatoms which are present in amine groups are also very good. However,amines react very readily with isocyanate groups which results in a veryfast rate of cure. In fact, the rate of cure attained utilizing aminesas the source of Zerewitinoff active hydrogen atoms can be too fast. TheZerewitinoff hydrogen present in carboxyl groups is far less active andpromotes a much slower rate of cure. For this reason, carboxyl groupsare not a preferred source of Zerewitinoff active hydrogen. The optimumrate of cure is believed to be attained when hydroxyl groups areutilized as the source of Zerewitinoff active hydrogen. Curatives can beutilized which contain at least two Zerewitinoff active hydrogen atoms.These compounds will typically have boiling points which are above thecure temperature of the rubber composition. In cases where the curativecontains at least two blocked isocyanate groups, the blocking groupswill also have a boiling point which is above the cure temperatureutilized in crosslinking the rubber composition.

Catalysts can be utilized in order to accelerate the reaction betweenthe Zerewitinoff active hydrogen and isocyanate groups. Such catalystsare of particular importance in cases where the blocking agent has avery high deblocking temperature. For instance, the utilization of suchcatalysts is of particular value in cases where 2-pyrrolidone isutilized as the blocking agent. Catalysts capable of speeding up boththe deblocking reaction and the reaction of the free isocyanate groupswith the Zerewitinoff active hydrogen can be utilized. For example, tinsalts, bismuth compounds, mercury compounds, tertiary amines, ironacetyl acetonate, cobalt acetyl acetonate and nickel acetyl acetonatecan be utilized as the catalyst. Tin salts such as dibutyltin dilaurate,dimethyltin dilaurate, dibutyltin diacetate, and dimethyltin diacetateare most preferred. Dialkyltin sulfides are also highly preferredcatalysts.

The rubber compositions of this invention will typically contain fromabout 0.001 moles to about 0.4 moles of blocked isocyanate groups per100 grams of polymer. The rubber compositions of this invention willpreferably contain from about 0.005 moles to about 0.1 moles of blockedisocyanate groups per 100 grams of polymer. Such rubber compositionswill more preferably contain from about 0.01 to about 0.03 moles ofblocked isocyanate groups per 100 grams of rubber. The rubbercompositions of this invention will typically have a molar ratio ofZerewitinoff active hydrogen atoms to blocked isocyanate groups of atleast about 0.5:1. Such rubber compositions will typically have a ratioof Zerewitinoff active hydrogen atoms to blocked isocyanate groups whichis within the range of about 0.6:1 to about 2:1. The ratio ofZerewitinoff active hydrogen atoms to blocked isocyanate groups in therubber composition will preferably be within the range of about 0.7:1 toabout 1.4:1. More preferably, the ratio of Zerewitinoff active hydrogenatoms to blocked isocyanate groups will be within the range of about0.8:1 to about 1.2:1. However, it should be noted that a verysubstantial excess of Zerewitinoff active hydrogen atoms over the amountof blocked isocyanate groups present typically is not detrimental inrubbers containing both pendant blocked isocyanate groups andZerewitinoff active hydrogen atoms.

In general, the elastomer containing one or both polymer bound curativescan be compounded using classical rubber compounding technology such asgiven by Long in his book "Basic Compounding and Processing of Rubber".There are several advantages associated with using the technologydisclosed in the instant invention. In typical rubber formulations,sulfur, and at least one accelerator is commonly used to affect thecure. To activate the sulfur, zinc oxide and stearic acid are usuallyemployed. In the cure system of the instant invention, one or both ofthe curatives is attached to the polymer. Thus, the total number ofingredients that must be added to the compound may be less with theinstant invention than with a conventional sulfur cure. This leads togreater product uniformity because there are fewer items to weight andpotentially fewer places to misweigh ingredients in the compoundingstep. Additionally, the non-sulfur crosslinks may have better stabilityto aging than the sulfur crosslinks.

The following examples are merely for the purpose of illustration andare not to be regarded as limiting the scope of the invention or themanner in which it can be practiced. Unless specifically indicatedotherwise, parts and percentages are given by weight.

EXAMPLE 1

General Recipes and Procedures for

Incorporation of C/T or HEMA into NBR

Two types of functionally substituted NBR rubbers (nitrile rubbers) wereprepared for cure via urethane chemistry. One contained monomer units ofcaprolactam/TMI (C/T) adduct: ##STR8##

The other contained units of β-hydroxyethyl methacrylate (HEMA). The C/Tmonomer is a white crystalline compound having a melting point of 59-62°C. The same general redox recipe was used for copolymerization of bothof these compounds into NBR and is shown in Table I as Recipes A and B.

                  TABLE I                                                         ______________________________________                                        Ingredient           A         B                                              ______________________________________                                        Deionized water      194.0     198.5                                          Potassium soap of hydrogenated                                                                     5.00      2.50                                           mixed fatty acids                                                             Na.sub.3 PO.sub.4 12H.sub.2 O                                                                      0.20      0.20                                           Diisopropyl xanthogen disulfide                                                                    1.50      --                                             (DIXIE)                                                                       C.sub.12 -C.sub.14   See Table II                                             p-menthane hydroperoxide (50 + %)                                                                  .08       .09                                            Butadiene-1,3        66.0      66.0                                           Aliphatic mercaptans See Table II                                             Acrylonitrile        See Table II                                             C/T                  See Table II                                             HEMA                 See Table II                                             Add through septum to above air free                                          systems:                                                                      FeSO.sub.4 7H.sub.2 O                                                                              .0041     .001                                           H.sub.2 SO.sub.4     .007      .007                                           Sodium ethylene diamine tetraacetate                                                               .024      .006                                           (38% aq solution)                                                             H.sub.2 O, soft      6.0       1.50                                           ______________________________________                                    

The polymerizations were run in quart bottles at 65° F. After reachingthe desired conversion level, the polymerizations were shortstopped withan aqueous solution containing 0.3 parts of sodium dimethyldithiocarbamate and 0.04 parts of N,N-diethylhydroxylamine.

NBR/caprolactam/TMI adduct copolymer productive stocks were prepared byblending all the components listed below in an unheated Brabender in aone pass mix. The mixes were blended for about 7 minutes at 80 rpm. Themaximum temperature developed during mixing were between 220-223° F.(104-106° C.). The blended stock was cured in a hydraulic press in stripmolds using the conditions used in Table III.

In one instance, DIXIE was used as a chain transfer agent forcopolymerization of C/T. In the others a tertiary aliphatic mercaptancontaining from 12 to 14 carbon atoms (Sulfole™ 132) was used as thechain transfer agent for copolymerization of either C/T or HEMAmonomers. Data relating to the monomer charge level or polymerizationtime on the degree of monomer incorporation are indicated in Table II.

Portions of NBR copolymers to be analyzed were prepared by coagulationof latex into isopropyl alcohol, washing small pieces of coagulum twiceeach successively with deionized water and isopropyl alcohol and vacuumdrying.

C/T content of NBR copolymers was determined by nmr analysis ofperdeutero acetone solutions on the basis of aromatic C-H bond content.C/T content of other copolymers was calculated on the basis of infraredtransmittance data. A known concentration of copolymer was analyzed andthe carbonyl absorption at 1706 cm⁻¹ was compared to a calibrationcurve.

The HEMA segmer content of NBR copolymers was determined by acetylationof a toluene solution of polymer with an acetic anhydride/pyridinemixture and titrating the residual acetic anhydride.

All of the rubbers made in runs 1-9 were soluble in both methyl ethylketone and toluene.

NBR/HEMA copolymers from runs 7 and 8 of Table II were similarlycompounded and cured using different levels of a caprolactam-blockeddiisocyanate with the structure: ##STR9## under varying cure conditions.Physical properties obtained by cures are indicated respectively inTables III and IV.

                                      TABLE II                                    __________________________________________________________________________    Incorporation of C/T or HEMA into NBR                                         Polymerization Run Number                                                     Parameters     1  2  3  4  5  6  7  8  9                                      __________________________________________________________________________    Recipe (Table 1)                                                                             A  A  B  B  B  B  B  B  B                                      Parts Charged:                                                                Acrylonitrile  27.5                                                                             27.5                                                                             27.5                                                                             27.5                                                                             27.5                                                                             26.0                                                                             30.0                                                                             30.0                                                                             28.0                                   DIXIE          1.50                                                                             1.50                                                                             -- -- -- -- -- -- --                                     RSH            -- -- 0.90                                                                             0.78                                                                             0.78                                                                             0.78                                                                             0.90                                                                             0.90                                                                             1.10                                   C/T            6.50                                                                             6.50                                                                             6.50                                                                             6.50                                                                             6.50                                                                             8.00                                                                             -- -- --                                     HEMA           -- -- -- -- -- -- 4.00                                                                             4.00                                                                             6.00                                   Conversion, %  64 74 76 83 87 -- 68 75 --                                     Polymerization Time                                                                          10 13 9  9.5                                                                              11 -- 9  10 --                                     @ 65° F., hours                                                        Polymerization Characteristics:                                               Mooney, ML4/212° F.                                                                   -- -- -- 24 34 29 -- -- 36                                     Parts C/T Bound:                                                              By NMR         -- 4.8                                                                              3.1                                                                              -- -- -- -- -- --                                     By IR          -- -- -- 4.5                                                                              4.5                                                                              5.6                                                                              -- -- --                                     Parts HEMA Bound:                                                             (Titration)    -- -- -- -- -- -- -- 1.88                                                                             3.87                                   __________________________________________________________________________

                                      TABLE III                                   __________________________________________________________________________    Compound           A   B    C    D    E   F                                   __________________________________________________________________________    Polymer from run # 2   3    3    3    3    3                                  Weight polymer     100.0                                                                             100.0                                                                              100.0                                                                              100.0                                                                              100.0                                                                              100.0                              ISAF Black         45.0                                                                              45.0 45.0 45.0 45.0 45.0                               Irganox 1076       1.0 1.0  1.0  1.0  1.0  1.0                                Tetramethylene glycol                                                                            0.75                                                                              0.49 0.49 0.53 --   --                                 Hydroxy terminated polytetramethylene                                                            --  --   --   --   29.8 29.8                               oxide (equivalent wt. 2520)                                                   Cure Temp., °F./time, min.                                                                350/25                                                                            350/30                                                                             350/30                                                                             350/30                                                                             350/30                                                                             380/30                                                         + 380/20                                          Vulcanizate Properties:                                                       Tensile strength, psi                                                                            (a) 2700 2140 3300 2820 2870                               Elongation %           450  400  510  200  200                                100% Modulus           250  250  240  850  890                                Shore A Hardness       64   64   63   69   68                                 Volume swell in ASTM oil, after                                                                      25.2 26.9 22.4 21.5 20.9                               70 hours at 300° F. (149° C.), %                                __________________________________________________________________________     (a) Vulcanizate porous because of gas evolution                          

                  TABLE IV                                                        ______________________________________                                        Cure of NBR Containing Hydroxy Groups                                         with a Blocked Diisocyanate                                                   Compound No.         G         H                                              Polymer from run #   8         9                                              ______________________________________                                        Weight of Polymer    100.0     100.0                                          ISAF black           45.0      45.0                                           Irganox 1076         1.0       1.0                                            Caprolactam blocked isophorone                                                                     7.1       14.7                                           diisocyanate                                                                  Cure Conditions F/min                                                                              350/15    350/30                                         Vulcanizate Properties:                                                       Tensile Strength, psi                                                                              1180      1590                                           Elongation, %        230       170                                            100% Modulus         480       940                                            Shore A Hardness     73        73                                             Volume Swell in ASTM #3 oil, after                                                                 22.2      21.2                                           70 hours at 300° F. (149° C.), %                                ______________________________________                                    

The data of Tables III and IV illustrate several features of thevulcanization process. Use of diisopropyl xanthogen disulkfide as achain transfer agent leads to porous vulcanizates (Compound A). This isprobably caused by elimination of carbon oxysulfide from the ends of thepolymer chain. Also, vulcanizates can be obtained by either binding theblocked isocyanate to the rubber and curing with a diol (Compounds B-F),or by binding the alcohol functionality to the polymer and curing with ablocked isocyanate (Compounds G-H).

                  TABLE V                                                         ______________________________________                                        Preparation of a Hydroxy functionalized SBR                                   Run Number              10                                                    ______________________________________                                        Deionized water         190.00                                                Potassium Phosphate     0.42                                                  Potassium Stearate      5.00                                                  Mixture of C-12 mercaptans                                                                            0.35                                                  p-menthane hydroperoxide (50%)                                                                        0.05                                                  Hydroxypropyl methacrylate (HPMA)                                                                     4.00                                                  Styrene                 26.00                                                 Butadiene               70.00                                                 Activator solution:                                                           iron (II) sulfate heptahydrate                                                                        0.007                                                 Sodium EDTA (38% aqueous solution)                                                                    0.04                                                  sulfuric acid/water (pH 5)                                                                            10.00                                                 Sodium formaldehyde sulfoxylate                                                                       0.03                                                  ______________________________________                                    

Table V gives the properties of an SBR containing hydroxypropylmethacrylate.

The emulsion was polymerized in the absence of oxygen at 50° F. (10° C).After polymerizing the emulsion for 8 hours, 68% of the monomer chargewas converted. A 10% aqueous solution containing 0.3 parts of sodiumdimethyldithiocarbamate and 0.04 parts of N,N-diethyl hydroxylamine wasadded to shortstop the reaction. 2.0 parts per hundred monomer of a 50%emulsion of Wingstay® C. (a commercial antioxidant) was added tostabilize the rubber to drying. The emulsion was coagulated and dried at150° F. (66° C.) in a circulating air oven. The rubber contained 4.1%bound hydroxypropyl methacrylate.

The rubber was vulcanized in the following recipes:

    ______________________________________                                        Compound No.      I        J        K                                         ______________________________________                                        Rubber (from run #10)                                                                           100.00   100.00   100.00                                    ISAF black        45.00    45.00    45.00                                     Processing oil    10.00    10.00    10.00                                     Dibutyltindilaurate                                                                             0.05     0.05     0.05                                      (catalyst)                                                                    Caprolactam blocked TMXDI                                                                       5.78     6.52     7.26                                      Vulcanizate Properties for Cures at 350° F. for 35                     minutes:                                                                      Tensile strength, psi                                                                           1510     1960     2100                                      Elongation, %     630      640      590                                       Shore A Hardness  57       59       62                                        ______________________________________                                    

The data from compounds I-K illustrate that the concept of curing rubbercontaining Zerewitinoff active hydrogens with blocked diisocyanates isapplicable to SBR (styrene-butadiene rubber) as well as nitrile rubber.

                  TABLE VI                                                        ______________________________________                                        Preparation of Rubbers Containing both Blocked                                Isocyanate Functionality and Hydroxyl Functionality                           Run Number         11      12       13                                        ______________________________________                                        Deionized water    200.0   200.0    200.0                                     Sodium Dodecylbenzene                                                                            2.0     2.0      2.0                                       sulfonate                                                                     Sodium persulfate  0.4     0.4      0.4                                       Sodium phosphate dodecahydrate                                                                   0.5     0.5      0.5                                       Pyrrolidone-blocked TMI                                                                          5.5     5.5      5.5                                       Styrene            22.3    21.1     21.5                                      Hydroxypropyl methacrylate                                                                       2.2     2.6      3.0                                       Mixture of tertiary                                                                              0.38    0.38     0.38                                      dodecylmercaptans                                                             Butadiene          70.0    70.0     70.0                                      Hours of Polymerization                                                                          7.5     7.0      7.0                                       at 125° F. (52° C.)                                             % Conversion       79.0    79.0     82.0                                      Parts pyrrolidinone-blocked                                                                      3.7     3.6      3.4                                       TMI bound to the polymer                                                      Parts Bound Hydroxypropyl                                                                        4.7     6.9      4.8                                       Methacrylate                                                                  bound to the polymer                                                          ______________________________________                                    

The polymerizations were shortstopped by addition of an aqueous solutionof dimethyldithiocarbamate and diethylhydroxylamine. After excessmonomers were removed by steam stripping, 0.5 phr Wingstay® L/0.5 phrtriarylphosphite dispersion was added to the latex. The latex wascoagulated and dried in a circulating air oven at 140-150° F. (60-66°C).

The rubbers were compounded in the following formulations:

    ______________________________________                                        Compound No.     L        M         N                                         ______________________________________                                        Rubber from run #                                                                              11       12        13                                        Weight of rubber 100.0    100.0     100.0                                     ISAF black       50.0     50.0      50.0                                      Aromatic Oil     10.0     10.0      10.0                                      Wingstay ® L (antioxidant)                                                                 0.5      0.5       0.5                                       Dibutyltin dilaurate catalyst                                                                  0.05     0.05      0.05                                      Cure Conditions °F./minutes                                                             390/35   390/35    390/35                                    Vulcanizate Properties:                                                       Tensile Strength, psi                                                                          2600     2550      2500                                      Elongation       550      540       490                                       300% Modulus     1200     1300      1350                                      Shore A Hardness 59       60        61                                        ______________________________________                                    

Thus, the data in Table VI indicate that polymers containing both theblocked isocyanate and the hydroxyl group can be vulcanized without theaddition of any further curatives.

EXAMPLE 14

In this experiment a self-stabilized styrene-butadiene rubber containingboth blocked isocyanate functionalities and hydroxyl functionalities wassynthesized. The redox recipe utilized in the polymerization containedthe following ingredients (shown in parts by weight):

    ______________________________________                                        Deionized water        195.0                                                  Sodium dodecylbenzene sulfonate                                                                      2.5                                                    Potassium phosphate    0.45                                                   Pyrrolidinone blocked TMI                                                                            6.7                                                    N-(4-anilinophenyl)methacrylamide                                                                    1.4                                                    Styrene                19.3                                                   Hydroxypropyl methacrylate                                                                           2.6                                                    Tertiary dodecylmercaptans                                                                           0.33                                                   1,3-butadiene          70.0                                                   ______________________________________                                    

as an activator system:

    ______________________________________                                        Iron (II) sulfate heptahydrate                                                                       0.0068                                                 Sodium EDTA (38% aqueous solution)                                                                   0.015                                                  Sulfuric acid/water solution (pH = 5)                                                                10.0                                                   Sodium formaldehyde sulfoxylate                                                                      0.04                                                   p-menthane hydroperoxide                                                                             0.06                                                   ______________________________________                                    

The emulsion made was polymerized in the absence of oxygen at 65° F.(18.5° C.). After allowing the polymerization to continue for 9.5 hours,75% of the monomer charge was converted. A 10% aqueous solutioncontaining 0.3 parts of sodium dimethyldithio carbamate and 0.04 partsof N,N-diethylhydroxyl amine was added to shortstop the reaction. Theemulsion was coagulated and dried at 150° F. (66° C.) in a circulatingair oven. The resulting dried polymer was soluble in methylene chlorideand chloroform. Infrared analysis of a solution cast film of the polymerindicated that it contained hydroxyl, blocked isocyanate and antioxidantfunctionalities.

EXAMPLE 15

In this experiment an additional self-stabilized styrene-butadienerubber containing both blocked isocyanate functionalities and hydroxylfunctionalities was made. The emulsion utilized in the polymerizationcontained the following ingredients (shown in parts by weight):

    ______________________________________                                        Deionized water        198.5                                                  Sodium phosphate       0.2                                                    Potassium stearate     2.5                                                    Pyrrolidinone blocked TMI                                                                            5.9                                                    N-(4-anilinophenyl)methacrylamide                                                                    1.4                                                    Acrylonitrile          24.2                                                   Hydroxypropyl methacrylate                                                                           2.5                                                    Tertiary dodecyl mercaptans                                                                          0.5                                                    1,3-butadiene          66.0                                                   ______________________________________                                    

as an activator system:

    ______________________________________                                        Iron (II) sulfate heptahydrate                                                                       0.002                                                  Sodium EDTA (38% aqueous solution)                                                                   0.0045                                                 Sulfuric acid/water solution (pH = 5)                                                                3.0                                                    Sodium formaldehyde sulfoxylate                                                                      0.03                                                   p-menthane hydroperoxide                                                                             0.09                                                   ______________________________________                                    

The emulsion was polymerized in the absence of oxygen at 65° F. (18.5°C). After 3 hours of polymerization time, 75% of the monomer charge wasconverted to polymer. A 10% aqueous solution containing 0.3 parts ofsodium dimethyldithiocarbamate and 0.04 parts ofN,N-diethylhydroxylamine was added to shortstop the polymerization. Thelatex was coagulated and air dried at 150° F. (66° C). Infrared analysisof a cast film of the polymer indicated the inclusion of hydroxyl,blocked isocyanate, and N,N-anilinophenyl methacrylamidefunctionalities.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in this art that various changes and modifications can be madetherein without departing from the scope of the invention.

What is claimed:
 1. A rubber composition which can be crosslinked byheating which is comprised of (1) at least one dry rubber having pendantblocked isocyanate groups bound thereto; and (2) at least one compoundwhich contains at least 2 Zerewitinoff active hydrogens.
 2. A rubbercomposition which can be crosslinked by heating which is comprised of(1) at least one dry rubber having Zerewitinoff active hydrogens boundthereto; and (2) at lest one compound having at least 2 blockedisocyanate groups bound thereto.
 3. A rubber composition which can becrosslinked by heating which is comprised of polymer chains having (1)pendant blocked isocyanate groups bound thereto; and (2) Zerewitinoffactive hydrogens bound thereto, wherein the rubber composition is dry.4. A process for curing the rubber composition specified in claim 1which comprises heating said rubber composition to an elevatedtemperature.
 5. A process for curing the rubber composition specified inclaim 2 which comprises heating the rubber composition to an elevatedtemperature.
 6. A process for curing the rubber composition specified inclaim 3 which comprises heating said rubber composition to an elevatedtemperature.
 7. A rubber composition as specified in claim 1 whereinsaid Zerewitinoff active hydrogens are present in a moiety selected fromthe group consisting of hydroxyl groups, amine groups, carboxyl groups,and thiol groups.
 8. A rubber composition as specified in claim 1wherein said Zerewitinoff active hydrogen is present in a hydroxylgroup.
 9. A rubber composition as specified in claim 1 wherein thependant blocked isocyanate groups are derived fromm-isopropenylα,α-dimethyl benzylisocyanate.
 10. A rubber composition asspecified in claim 9 wherein said isocyanate groups are blocked withcyclic amides.
 11. A rubber composition as specified in claim 10 whereinsaid cyclic amide is 2-pyrrolidone.
 12. A rubber composition asspecified in claim 10 wherein said cyclic amide is caprolactam.
 13. Arubber composition as specified in claim 11 wherein the compound whichcontains at least two Zerewitinoff active hydrogens is tetramethyleneglycol.
 14. A rubber composition as specified in claim 12 wherein thecompound which contains at least two Zerewitinoff active hydrogens istetramethylene glycol.
 15. A rubber composition as specified in claim 1which further comprises a catalyst selected from the group consisting ofdibutyltin dilaurate, dimethyltin dilaurate, dibutyltin diacetate, anddimethyltin diacetate.
 16. A rubber composition as specified in claim 1wherein the rubber having pendant blocked isocyanate groups boundthereto has from about 0.005 to about 0.1 moles of blocked isocyanategroups per hundred grams of total weight.
 17. A rubber composition asspecified in claim 16 wherein the ratio of Zerewitinoff active hydrogencontaining groups to blocked isocyanate groups in the rubber compositionis within the range of about 0.6:1 to about 2:1.
 18. A rubbercomposition as specified in claim 1 wherein the rubber having pendantblocked isocyanate groups is a nitrile rubber.
 19. A rubber compositionas specified in claim 1 wherein the rubber having pendant blockedisocyanate groups is a styrene-butadiene rubber.
 20. A rubbercomposition as specified in claim 3 wherein the polymer chains containrepeat units which are derived from β-hydroxyethyl methacrylate.